TutorCommandExecutor crashed on empty lines

[jurgenvinju]

This is an example:

```rascal-shell
import lang::csv::IO;
rel[int position, str artist, str title, int year] R1 = {
  <1,"Eagles","Hotel California",1977>,
  <2,"Queen","Bohemian rhapsody",1975>,
  <3,"Boudewijn de Groot","Avond",1997>
};
// we can write the CSV with a header row:
writeCSV(#rel[int position, str artist, str title, int year], R1, |tmp:///ex1a.csv|);

// or write it without the header row:
writeCSV(#rel[int, str, str, int], R1, |tmp:///ex1b.csv|, header = false, separator = ";");
```

The empty line after the first writeCSV breaks the repl simulator by throwing a ParseError unexpectedly. The real REPL goes to the first continuation prompt on an empty line. If that is right, then the TutorCommandExecutor should simulate this.